Update pdf-endpoint.mdx (#26129)

fix code block

Author: kathayl

src/content/docs/browser-rendering/rest-api/pdf-endpoint.mdx

@@ -192,7 +192,8 @@ curl -X POST 'https://api.cloudflare.com/client/v4/accounts/<accountId>/browser-
         "left": "30px"
       },
       "timeout": 30000
-    }
+    }`
+```
 
 <Render
   file="setting-custom-user-agent"